Conventional controls for forced air heating and cooling systems often provide for delayed startup of the fan drive motor at a single operating speed and delayed shutdown of the drive motor from a single operating speed after shutdown of the heat exchangers of the heating/cooling system. Conventional controls are designed to minimize unpleasant cold or hot drafts of air and to capture residual heat/cooling effect. However, changing motor speed abruptly from a deenergized or shutoff state to full speed usually generates unpleasant noise, does not preclude stratification of air in the system ductwork or in the space being heated or cooled, nor does such operation maximize the capture of residual heat/cooling effect of the system heat exchange equipment.
Control systems have been developed for forced air heating/cooling systems wherein the indoor space air circulating fan drive motor is driven at reduced speed for a period of time during startup and at a reduced speed for a period of time during the run-on or shutdown phase of the heating/cooling system operating cycle. Again, this type of control system does not minimize the stratification of warm or cold air in the ductwork or the space being heated or cooled nor does such a system maximize the capture of residual heating/cooling effect.
Prior patent applications Ser. Nos. 09/570,880 and 08/801,560 (now U.S. Pat. No. 6,070,660) assigned to the assignee of the present invention and referenced hereinabove are directed to an improved fan or blower drive motor control system and method for forced air heating/cooling systems wherein the fan drive motor speed is continuously varied during a starting phase and a shutdown phase of operation of the heating/cooling system. In one embodiment of the control system disclosed in the aforementioned patent application and patent, the system senses temperature in the airflow circuit of the heating/cooling system and prevents premature or unwanted operation of the fan drive motor. The present invention is directed to improvements in control systems of that general type. The subject matter of U.S. Pat. No. 6,070,660 issued Jun. 6, 2000 to Howard P. Byrnes, et al. is incorporated herein by reference, in its entirety.